This invention relates to prostacyclin I.sub.1 derivatives and to a process for preparing them.
Prostacyclins are a class of organic compounds related to the well-known prostaglandins. The parent compound first identified as prostacyclin is represented by the formula ##STR2## and is named (5Z)-9-deoxy-6,9.alpha.-epoxy-.DELTA..sup.5 -PGF.sub.1 or, for brevity, PGI.sub.2. See R. A. Johnson et al., J. Am. Chem. Soc. 99, 4182 (1977) and Anonymous, Prostaglandins 13, 375 (1977).
As with prostaglandins, the formula as drawn represents a particular optically active isomer. Broken line attachments to a ring or side chain indicate substituents in alpha configuration, i.e. below the plane of the ring or side chain. Heavy solid line attachments indicate substituents in beta configuration, i.e. above the plane.
Prostacyclin I.sub.1, as used herein, identifies 5,6-dihydroprostacyclins represented by the formula ##STR3## of which there are two isomers identified as (6S) or (6.beta.)-PGI.sub.1 and (6R)(or 6.alpha.)-PGI.sub.1.
Reference to 6-hydroxy PGI.sub.1 hemiketals has been made previously. See Johnson et al., cited above and Belgian Pat. No. 851,122 abstracted in Derwent Farmdoc No. 57511Y.